1. Field of the Invention
The present invention relates to an optical sensor module including an optical waveguide unit and a board unit mounted with an optical element.
2. Description of the Related Art
As shown in FIGS. 9A and 9B, an optical sensor module is produced by individually producing an optical waveguide unit W0 including an under-cladding layer 71, a core 72 and an over-cladding layer 73 provided in this order, and a board unit E0 including an optical element 82 mounted on a substrate 81, and then bonding the board unit E0 to an end portion of the optical waveguide unit W0 with an adhesive or the like with the core 72 of the optical waveguide unit W0 in alignment with the optical element 82 of the board unit E0. In FIGS. 9A and 9B, a reference character 75 designates a base, and a reference character 85 designates a sealing resin.
The alignment between the core 72 of the optical waveguide unit W0 and the optical element 82 of the board unit E0 is generally achieved with the use of a self-aligning machine (see, for example, JP-A1-HEI5 (1993)-196831). In this self-aligning machine, the optical waveguide unit W0 is fixed to a stationary stage (not shown) and the board unit E0 is fixed to a movable stage (not shown) for the alignment. Where the optical element 82 is a light emitting element, an alignment position (at which the core 72 is properly aligned with the optical element 82) is determined, as shown in FIG. 9A, by changing the position of the board unit E0 relative to one end face (light inlet) 72a of the core 72 with light H1 being emitted from the light emitting element, monitoring the amount of light outputted from the other end face (light outlet) 72b of the core 72 through a lens portion 73b provided at a distal end of the over-cladding layer 73 (monitoring a photovoltaic voltage developed across a light receiving element 91 provided in the self-aligning machine), and then defining a position at which the light amount is maximum as the alignment position. Where the optical element 82 is a light receiving element, the alignment position is determined, as shown in FIG. 9B, by changing the position of the board unit E0 relative to the one end face 72a of the core 72 with a predetermined amount of light (light emitted from a light emitting element 92 provided in the self-aligning machine and transmitted through the lens portion 73b provided at the distal end of the over-cladding layer 73) H2 being inputted from the other end face 72b of the core 72 and outputted through a tail end portion 73a of the over-cladding layer 73 from the one end face 72a of the core 72, monitoring the amount of light received by the light receiving element (monitoring a photovoltaic voltage), and defining a position at which the light amount is maximum as the alignment position.
The alignment achieved by utilizing the self-aligning machine is highly accurate, but is unsuitable for mass production with the need for labor and time.
There is an optical sensor module which permits easy alignment without the need for the aforementioned machine and labor (Japanese Patent Application No. 2009-180723). In the optical sensor module, as shown in plan in FIG. 10A and in perspective in FIG. 10B with its right end viewed from an upper right side, an optical waveguide unit W1 includes an over-cladding layer 43 having opposite side extension portions (upper and lower portions on a right side in FIG. 10A) which extend in a core axial direction (in a rightward direction in FIG. 10A) and are free from a core 42. The extension portions 44 respectively have board unit engaging vertical grooves 44a provided in pair in proper positions thereof relative to a light transmission face (one end face) 42a of the core 42 as extending thicknesswise of the optical waveguide unit W1. On the other hand, a board unit E1 includes engagement portions 51a provided in proper positions relative to an optical element 54 in left and right edge portions (laterally opposite edge portions) thereof to be brought into fitting engagement with the vertical grooves 44a. 
In the optical sensor module, the board unit E1 is coupled to the optical waveguide unit W1 with the engagement portions 51a of the board unit E1 in fitting engagement with the vertical grooves 44a of the optical waveguide unit W1. Here, the vertical grooves 44a of the optical waveguide unit W1 are designed so as to be located in the proper positions with respect to the light transmission face 42a of the core 42, and the engagement portions 51a of the board unit E1 are designed so as to be located in the proper positions with respect to the optical element 54. Therefore, the fitting engagement between the vertical grooves 44a and the engagement portions 51a permits self-alignment between the core 42 and the optical element 54. In FIGS. 10A and 10B, a reference character 45 designates a base, and a reference character 45a designates a through-hole provided in the base 45 for receiving the board unit E1. Further, a reference character 51 designates a shaped substrate having the engagement portions 51a, and a reference character 55 designates a sealing resin.
Thus, the optical sensor module permits self-alignment between the core 42 of the optical waveguide unit W1 and the optical element 54 of the board unit E1 without the aligning operation. This eliminates the need for the time-consuming aligning operation, permitting mass production of the optical sensor module at higher productivity.
In recent years, the optical waveguide unit W1 of the optical sensor module has been required to have a reduced width. If the width of the optical waveguide unit W1 is reduced, however, the extension portions 44 cannot be provided in the opposite side portions, but a single extension portion 44 is provided in one of the opposite side portions. In this case, a single board unit engaging vertical groove 44a is provided in the extension portion 44. Even if the board unit E1 is in fitting engagement with the vertical groove 44a, the board unit E1 is unstably supported at a single engagement portion 51a thereof. Therefore, there is a possibility that the proper alignment cannot be achieved even with the board unit E1 in fitting engagement with the vertical groove 44a. 